1. Field of the Invention
The present invention relates to a method for producing a cleaning blade and specifically to a method for producing a cleaning blade for electrophotographic apparatuses.
2. Description of the Related Art
In general, even after a toner image formed on the surface (outer peripheral surface) of an electrophotographic photosensitive member (hereafter also simply referred to as “a photosensitive member”) has been transferred onto a transfer material or an intermediate transfer member or even after the toner image has been further transferred onto a transfer material from the intermediate transfer member, part of toner easily remains on the surfaces of the photosensitive member and/or the intermediate transfer member. Therefore, the toner remaining on the surfaces of the photosensitive member and/or the intermediate transfer member needs to be removed. This removal is normally performed with a cleaning blade.
A cleaning blade is normally attached to a metal holder in an electrophotographic apparatus and used in a fixed state.
A cleaning blade is usually made of a urethane rubber having high wear resistance and a good property for permanent deformation.
An electrophotographic apparatus is often used in an environment of 5° C. to 40° C.
However, the elastic coefficient of urethane rubber tends to suddenly change near room temperature (10° C. to 25° C.) and thus urethane rubber is a material whose flexibility, strength, and the like required for cleaning are prone to be dependent on temperature. The temperature dependence is estimated using tan δ obtained from a dynamic viscoelasticity test and the peak temperature of tan δ. Many urethane rubbers have a peak temperature of tan δ near room temperature. Near the peak temperature of tan δ, the elasticity sharply increases and the flexibility tends to decrease. Thus, the peak temperature of tan δ can be as low as possible and tan δ can change in a gentle curve from a low temperature to a high temperature.
The hardness of the urethane rubber can be in the range of 65° to 85° in terms of cleaning performance. The higher the value of the hardness is, the harder the urethane rubber becomes.
Regarding the permanent deformation due to compression of urethane rubber, the contact pressure of an edge of the cleaning blade onto the surface of the photosensitive member or intermediate transfer member tends to decrease as the permanent deformation due to compression increases. Furthermore, it becomes difficult for an edge of the cleaning blade to uniformly come into contact with the surface of the photosensitive member or intermediate transfer member as the permanent deformation due to compression increases. Therefore, the permanent deformation due to compression can be as low as possible. In view of the wear resistance of urethane rubber, the permanent deformation due to compression can also be as low as possible.
Various urethane rubbers have been studied and, in particular, a method for improving the characteristics of a cleaning blade made of urethane rubber by adding an isocyanurate bond to the urethane rubber is being studied. The isocyanurate bond has a six-membered ring structure in which three isocyanates are trimerized. That is, the urethane rubber having an isocyanurate bond is a urethane rubber having a structure cross-linked with an isocyanurate bond. Therefore, the urethane rubber having an isocyanurate bond has high stiffness (low permanent deformation due to compression) and high thermal decomposition temperature (high resistance to thermal decomposition, high heat resistance) and thus is a good material for cleaning blades.
It is described in Japanese Patent Laid-Open No. 2008-250311 that a small amount of isocyanurating catalyst (isocyanate trimerization catalyst) is added to a urethane rubber raw material, a reaction is caused to synthesize a urethane rubber having an isocyanurate bond, and the urethane rubber is used for cleaning blades. It is also described that the use of the synthesized urethane rubber achieves high cleaning performance in a low-temperature environment and suppresses the chattering and curling in a high-temperature environment. It is also described that, in the urethane rubber, the ratio (IRCN(I)/IRCN(U)) of the infrared absorbance IRCN(I) of a C—N bond in an isocyanurate bond to the infrared absorbance IRCN(U) of a C—N bond in a urethane bond is 0.30 or more and 0.90 or less.
It is described in Japanese Patent Laid-Open No. 2008-9400 that a long-chain polyol having a number-average molecular weight of 1500 to 3800, an isocyanate, and an isocyanurate derivative having two or more OH groups are caused to react with each other to obtain a rubber-like elastic body (urethane rubber). It is also described that the obtained rubber-like elastic body is used for a cleaning blade to improve the wear resistance of the cleaning blade. It is also described that 0.5 to 15 parts of the isocyanurate derivative is contained relative to 100 parts of the long-chain polyol.
However, if a large amount of isocyanurate catalyst is used in the technology described in Japanese Patent Laid-Open No. 2008-250311, the rate of the synthesis reaction of the urethane rubber tends to increase. If the rate of the synthesis reaction of the urethane rubber excessively increases, gelation tends to occur on part of the isocyanurating catalyst. The gelation makes it difficult to obtain a cleaning blade uniformly made of urethane rubber. Therefore, a large amount of isocyanurating catalyst cannot be added and consequently it is difficult to increase the content of the isocyanurate bond in the urethane rubber.
The technology described in Japanese Patent Laid-Open No. 2008-9400 is a technology in which the isocyanurate derivative is added as a chain extender and a cross-linking agent. Use of a large amount of isocyanurate derivative easily causes the aggregation of the isocyanurate derivative, which poses a problem such as a difficulty in synthesizing the urethane rubber. Furthermore, use of the isocyanurate derivative in the synthesis of the urethane rubber increases the cost. Since the isocyanurate derivative has a high melting point, the temperature at which raw materials for synthesizing the urethane rubber are mixed needs to be increased (e.g., 140° C. or higher), which easily causes the gelation of the raw materials. Moreover, the molding temperature of a cleaning blade made of urethane rubber needs to be increased (e.g., 150° C. or higher), which tends to increase the production cost of cleaning blades.